Haskell

Introduction

This is my first dip into Haskell, just felt like trying it. Haskell is a purely functional programming language. rather than a declarative language. I.E. it is a declarative language rather than imperative. With declarative, you tell the language what the thing is rather than how to do the thing.

Features

Lazy

Haskell is a programming lazy language and only evaluates on usage. E.g. only evaluates the first 10

let infiniteList =  [1..]
take 10 infiniteList

Modules

Starting to look a lot like Lisp. This next bit shows how you can combine various functions of your own to produce and output

let double = x = x * 2
let increment x = x + 1
let doubleThenIncrement x = increment(double x)
doubleThenIncrement 10 -- Answer is 21

Statically Typed

With Haskell types are inferred

Hello World

Here we start with main and strange format but no curly brackets which is good.

main :: IO()
main = putStrLn "Hello World"

We build like gcc using

ghc hello.hs -o hello

Date Models

Types

• Numbers e.g. 1
• Chars e.g. "S"
• Boolean e.g. True, False
• List e.g. [1,2,3], [True, False, True]
• Tuple e.g. (1,2,3, "string, True)

List Comprehension

You can define a function and operate against a list like this

[x*2 | x <-[1..10]] -- Answer is [2,4,6,8,10,12,14,16,18,20]

Constructs

Pattern Matching

No surprises, and I love pattern matching

-- Pattern Matching
coffeeType :: String -> String
coffeeType "Epresso" = "Strong and bold"
coffeeType "Cappuccino" = "Frothy and delicious"
coffeeType "Filter" = "Watery and weak"
coffeeType _ = "I have no idea what that is"

main = do 
    print(coffeeType "Epresso")
    print(coffeeType "Cappuccino")
    print(coffeeType "Filter")
    print(coffeeType "Latte")